The program is involved in a study of the biology of bone marrow transplantation in animals and man. It is divided into four major program areas: (1) clinical trials; (2) immunobiology of transplantation; (3) interstitial pneumonia; (4) infectious disease. Clinical trials are directed to study in the role of transplantation in aplastic anemia, leukemia, and immunodeficiency diseases. Studies in progress include graft-rejection, graft-versus-host disease (GvHD), leukemia eradication, and prophylaxis of infection and interstitial pneumonia. Phase-1 trials are investigating fetal liver transplantation. A Phase-2 trial of autotransplantation is being conducted in patients with solid tumors. The program in immunobiology is directed towards the following areas: (1) antigens on and immunity to hematopoietic stem cells, (2) in vitro models of immunity to non-major histocompatibility complex (MHC) antigens and (3) in vitro induction of transplantation tolerance. Studies of interstitial pneumonia include an animal model of latent cytomegalovirus (CMV) infection, in vitro studies of immune response to CMV and other viruses, and a clinical trial of CMV prophylaxis. The program in infection prevention involves rapid diagnosis of fungal disease and the role of protected environments and granulocyte transfusions in transplantation.